read*_poll_timeout's final timeout parameter is in microseconds,
but the supplied arguments in fec_imx.c were in nanoseconds,
which might lead to barebox getting seemingly stuck in fec_halt
(loops for a thousand seconds instead of one).

I've tested this still works on an i.MX6D by copying a file over
TFTP and verifying the hash is correct.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>